The effect of the lathyrogen, beta-amino-pripionitrile (BAPN), on inhibition of dimethyl-benz (a) anthracene (DMBA)-induced rat breast tumors will be further studied. Preliminary findings suggest that under lathyritic conditions, the development and incidence of DMBA rat breast tumors are substantially reduced. The absence of the firm, well organized collagen matrix, which normally encapsulates this tumor, may allow more effective immunologic invasion by macrophages resulting in tumor retardation. Alternatively, beta-aminoprionitrile may be affecting the normal supply of hormone to this endocrine-dependent tumor. Female, Sprague-Dawley rats will be made lathyritic by dietary administration of BAPN (1%) either prior to or after administration of DMBA. The clinical course of tumor development will be assessed and compared to histologic evaluation of pituitary, adrenal and ovarian function. In addition, the estrogen receptor activity of the tumor cells will be monitored in the BAPN treated animals and compared to control values. These studies will determine if BAPN causes DMBA rat breast tumor inhibition by interfering with endocrine supply. Futhermore, the cell population will be characterized in the small DMBA tumors which result following simultaneous BAPN treatment to determine if there is increased macrophage infiltration causing tumor cytotoxicity. These studies are aimed at defining the role of collagen metabolism and structure in the biology of breast cancer.